Testing the socket_io @mqtt.on_connect() callback

app_test_socket_mqtt_connect.py

# Flask MQTT Web socket bridge
 
from flask_mqtt import Mqtt
import json
import eventlet
from flask import Flask,render_template 
from flask_socketio import SocketIO, emit
from flask_bootstrap import Bootstrap

eventlet.monkey_patch()

app = Flask(__name__)
app.config['SECRET'] = 'my-secret'
app.config['MQTT_BROKER_URL'] = 'localhost'      
app.config['MQTT_BROKER_PORT'] = 1883
app.config['MQTT_TLS_ENABLED'] = False  
app.config['TEMPLATES_AUTO_RELOAD'] = True

mqtt = Mqtt(app)
socketio = SocketIO (app)  
bootstrap = Bootstrap(app)

@app.route('/')
def index():
    return render_template('index.html')

@socketio.on('publish')
def handle_publish(json_str):
    data = json.loads(json_str)
    mqtt.publish(data['topic'], data['message'], data['qos'])

@socketio.on('subscribe')
def handle_subscribe(json_str):
    data = json.loads(json_str)
    mqtt.subscribe(data['topic'], data['qos'])

@socketio.on('unsubscribe_all')
def handle_unsubscribe_all():
    mqtt.unsubscribe_all()
    
@socketio.on('connect')
def on_socket_connect ():
    print ('Connected to socket client.')
    # mqtt.subscribe('mytopic')  

@mqtt.on_message()
def handle_mqtt_message(client, userdata, message):
    data = dict(
        topic=message.topic,
        payload=message.payload.decode(),
        qos=message.qos,
    )
    emit('mqtt_message', data=data)
    
# This is never called:
@mqtt.on_connect()  
def on_mqtt_connect (client, userdata, flags, rc):
    print ('Connected to MQTT broker.')
    mqtt.subscribe ('mytopic')   # this would be ideal
    print(mqtt.topics)
    
@mqtt.on_message()
def on_message(client, userdata, message):
    socketio.send (message.payload.decode())

if __name__ == '__main__':
    socketio.run(app, host='0.0.0.0', port=5000, use_reloader=False, debug=True)